Thermoelectric generator with fluid cooling



L A K E L A M K S THERMOELECTRIC GENERATOR WITH FLUID COOLING Filed Feb. 14 1 3nnentons aitorne Patented Dec. 14, 1948 THERMOELECTRIC GENERATOR WiTl-I FLUID COOLING Sidney K. Malek and Marvin R. Laing, Minneapolis, Minn., assignors to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a

corporation of Delaware Application February 14, 1944, Serial No. 522,369

7 Claims. 1

Our invention relates to a thermoelectric generator of the type known as a thermopile and more particularly to a thermopile having assoclated with it means for regulating the temperature of the cold junctions. As is well known by those skilled in the art, the extent of the potential difference generated by a thermopile is regulated by the difference in temperature between the hot and cold junctions. In the prior art a variety of means have been used to maintain a substantial difierential between hot and cold junctions, as for example, by air or water cooling. Such means required the use of a cumbersome arrangement of pipes or filled, with a desirable fluid is in thermal contact with the cold junctions and further arranged with a condensing means or other cooling means whereby the temperature of the cold junctions will be limited to a maximum temperature which may be defined by the boiling point of the fluid.

The principal object of our invention is to provide a thermoelectric generator with means whereby the temperature of the cold junctions may be regulated by having in thermal contact therewith a self-contained body of fluid whose boiling point is substantially lower than the average normal conductive temperature of the cold junctions when the generator is in operation.

Another object is to provide means for maintaining the cooling fluid which is in thermal contact with the cold junctions, at a temperature susbtantially below its boiling point.

Other objects and advantages will become apparent from the specification, and the appended drawings in which:

Figure 1 is an elevational view of a thermoplle whose cold Junctions are in thermal contact with one embodiment of a cooling means, the cooling-means being shown invertical section;

Figure 2 is a cross section taken along the'line 2-2 of Figure 1;

Figure 3 is a partial view of a modification of our invention;

Figure 4 is an enlarged sectional view of a modiiied cup element shown in'Figure 1.

Referring to Figures 1 and 2, the reference numeral l0 designates an insulating member which may be made of porcelain or other like material which serves as burner means.

Generally designated at 20 is a thermopile made up of a plurality of thermocouples 2|, each of which is formed of a pair of members 22 and 23 of materials of dissimilar thermoelectric characteristics, which may, for example, be iron and constantan. Each of the members is joined at the top 26 and bottom 25 to a dissimilar metal member as by welding, so as to form a continuous electric contact between the dissimilar members. A cap 26 of heat resistant metal, such as stainless steel, is placed over the top or hot j unction of each thermocouple to prevent oxidation at the point where thethermocouple is in contact with the A lower body or container 30 which is shown as being formed of insulating material but which might be formed of metal has a plurality of cups 3! mountci in its upper surface and extending into the interior thereof. cup members 3| are so mounted in the insulating material that they are not in. electrical contact with each other but new formed that the cold junction of each of the thermocouples is in thermal contact with the sides of the cup which contact may be further aided by welding or brazing the cold junctions within the cup members. In

Figure 4, is shown a modification of one of these hereinafter is placed within'the container 36 so as to nearly fill the same. When heated, the vapor may pass out through the pipe 33 into a condenser 34 which is preferably of the air cooled type and when the vapor is cooled to a liquid state it returns to the main body through the pipe 35. An extension of the pipe 33 into the condenser serves to prevent the gaseous fluid from obstructgas in one direction and the liquid in the other.

There are a number of liquids which could be used for the cooling agency and the selection Each of the thereof would depend upon the use and conditions of operation. Preferably the liquid should have a low electrical conductivity so that it would not have the tendency to create short circuits between the various cold junctions when used as shown in the modification of Figure 1. In addition to the non-conductive qualities, other desirable characteristics are chemical stability, a pH in the vicinity of 7.0, a low vapor pressure and a relatively high heat of vaporization. We have found that a liquid such as carbon tetrachloride is entirely satisfactory in that it has a very low.conductivity, it is chemically stable and is non-corrosive and furthermore it is non-combustible. The real criteria'in the selection of the cooling liquid, however, must reside in its boiling point, for if a liquid is used having an extremely high boiling point or one which is above the average normal operating temperature of the cold junctions the liquid will be incapable of rapid evaporation and therefore will lack the cooling qu lities needed to become efiective. For example, if the average normal temperature of the cold junctions is say 90 0., there would be no point in using water as a cooling agent for it would be heated to 90 C;, without boiling and it would thus serve no cooling purpose whatsoever, beyond its initially low starting temperature.

A modification of our invention is shown in Figure 3 wherein the cold junctions 25 are shown directly embedded in a solid material or an aggregate such as mica, ground lava or other solid substance 40, or a heat conducting liquid which should have the characteristic of having a low electricalconductlvity and'a high heat conductivity, such as oil, might be used in place of the solid substance. The container 4|, is shown as being made of insulating material or plastic but 'it might also be made of metal for in this modificatlon, the heat conducting material 40 could be of a low electrical conductive nature which is a characteristic of the materials described hereinbefore and in that case a metal container would be preferable because of its higher heat conducting capacity. A porcelain or glass member 42, in which the thermocouples are mounted, serves the same purpose as member III in Figures 1 and 2. The pipes 31 and 38 extend to a condenser (not shown) or other cooling means, in the same manner as in the previous modification, and likewise as previously mentioned, could be replaced by a single pipe serving the dual purpose of pass- -ing the gases to the condenser andthe liquid back to the main body.

The cooling fluid used in the modification shown in Figure 3, need not have the same nonconductive properties as that used in the modification of Figure 1. Here the cold junctions would normally be imbedded in a non-conducting aggregate or liquid and therefore the boiling point of the coolant would be the principal consideration and as previously mentioned it should be lower than the mean operating temperature of The most important featureof the condenser or other cooling means must be that it shall have sufllcient capacity to dissipate the heat which is transferred to it so as to maintain the temperature of the cooling liquid below the operating temperature of the cold junctions. The term operating temperature as used herein refers to the temperature resulting from heat transmitted by conduction through the thermopile from the hot junction area to the cold junction area, or the mean temperature of the cold junctions when heat is being applied to the hot junctions.

Although we have disclosed our present inventionas a thermopile controlled by a pilot flame and an air cooled condenser, it will be understood by those skilled in the art that this invention may assume any proportion and may utilize any source of heat without departing from the spirit of the invention;

What we claim to be new and desire to secure by Letters Patent are:

1. A thermoelectric generator, comprising in combination, a thermopile composed of a plurality of dissimilar members alternately joined at their opposite ends and arranged to form a hot junction and a cold junction, fuel burning means associated with said thermopile for applying heat to the hot junction portion of said members, a liquid container associated with said thermopile and mounted to surround only the cold junction portion of said members, said containers being partially filled with an evaporable liquid which is 'in thermal contact with the cold junction portion of said members to absorb heat conducted through the thermopile members from the hot junction portion, said liquid being characterized by having a boiling point which is substantially less than the mean operating temperature of the cold junction portion of said members when receiving heat from the hot junction portion, and a condenser operatively associated with said liquid container to cool and return to said container the evaporated portion of said liquid.

2. A thermoelectric generator, comprising in combination, a thermopile composed of a plurality of dissimilar members alternately joined at porting said dissimilar members about their center portion in such a manner as to form a hot junction area on one side of said insulator and a cold junction on the opposite side of said insulator, a fuel burner positioned adjacent said thermopile for applying heat to the hot junction area, a liquid container surrounding the cold junction area, said container being partially filled with an evaporable liquid which liquid is in thermal contact with said cold junction area, to

absorb heat conducted through the thermopile members from the hot junction area when receiving heat from the hot junction, said liquid being characterized by having a boiling point which is substantially less than the operating temperature of said cold junction area when receiving heat from the hot junction area, and a condenser operatively connected to said liquid container for condensing and returning to said container the evaporated portion of said liquid.

3. In a thermoelectric generator, a thermocouple composed of dissimilar metal members joined at one of their ends and supported to form a hot junction, an electrical conductor secured to the other end of each of said members, a mass of substance which is thermally conductive and electrically nonconductive surrounding each of the other ends of said members, a liquid container associated with said mass, said container being partially filled with a liquid in heat transfer relationship with said mass to absorb heat conducted through the thermocouple members from the hot junction, said liquid being characterized by having a boiling point which is substantially less than the operating temperature of said cold junction, a condenser associated with said liquid container and positioned above the liquid level therein for receiving and condensing the evapotainer surrounding the opposite extended joined ends of said strips, said container being partially filled with a liquid in thermal contact with the extended ends of said strips which are surrounded by said container to absorb heat conducted through the strips from-the heated ends thereof, said liquid being characterized by having a boiling point which is less than the boiling point of water and also less than the operating temperature of the joined ends of said strips which are surrounded by said liquid container when receiving heat from the heated ends of the strips, an air-cooled condenser associated with said liquid container and positioned above thenormal liquid level in said container, 9, first conduit for conducting liquid vapors from said container to said condenser, and a second conduit for conducting condensed liquid from said condenser to said container whereby liquid evaporation in said container will maintain the joined ends of said strips surrounded by said liquid at a temperature which is substantially less than the boiling point of water.

5.111 athermoelectric generator, a thermopile composed of a plurality of dissimilar members alternately joined at their opposite ends and arranged-to form a hot junction and a cold junction, a liquid container associated with said thermopile and mounted to surround only the cold juncduit connecting the upper interior portions of said container and condenser, and a second conduit extending between the lower interior portions of said container and condenser.

'6. In a thermoelectric generator, a thermocouple composed of dissimilar metal members joined at one of their ends and supported to form a hot junction, an electrical conductor secured to the other end of each of said members, a mass of thermally conductive and electrically nonconductive material surrounding each of the other ends of said members, a liquid container associated with said mass. said container being partially filled with a liquid in heat transfer retion portion of said members, said container being I partially filled with an evaporable liquid which through the thermopile members from the hotv junction, said liquid being characterized by having 7 a boiling point which is substantially less than the mean operating temperature of the cold junc- Number tion portion of said members when receiving heat from the hot junction, a vapor condenser, a conlationship with and surrounding a portion only of said mass to absorb heat conducted through the thermocouple members from the hot junction, said liquid being characterized by having a boiling point which is substantially less than the operating temperature of said cold junction when receiving heat from the .hot junction, a condenser associated with said liquid container and positioned above 7 the liquid level therein for receiving and condensing the evaporated liquid, a conduit establishing communication between the upper interior portions of said container and said condenser and conduit means connected between said container and said condenser for returning the condensed liquid to said container.

' '7. A thermocouple comprising a hot junction adapted to be heated; a cold junction; and means to cool said cold junction comprising a container made of dielectric heat-conducting material and partially filled with volatile liquid having a vaporizing temperature below the desired operating temperature of said cold junction when receiving REFERENCES CITED I The followingreferences are of record in the file of this patent:

- -UNITED STATES PATENTS Number Name Date 375,243 Acheson Dec. 20, 188'? 513,421 Rowland Jan. 23, 1894 528,924 Cox Nov. 13, 1894 615,541 Emanuel Dec. 6, 1888 FOREIGN PATENTS j Country Date Great Britain July 25, 1918 France June 30,1902

Hale Apr. 6, 1915 

